Method and device for sampling and analyzing interstitial fluid and whole blood samples

ABSTRACT

The invention disclosed in this application is a method and device for combining the sampling and analyzing of sub-dermal fluid samples, e.g., interstitial fluid or whole blood, in a device suitable for hospital bedside and home use. It is applicable to any analyte that exists in a usefully representative concentration in the fluid, and is especially suited to the monitoring of glucose.

RELATED APPLICATIONS

[0001] This application is a continuation of Application No. 10/166,487,filed Jun. 10, 2002, which is a continuation of Application No.09/536,235, filed Mar. 27, 2000.

FIELD OF THE INVENTION

[0002] The present invention relates to a method and device forcombining the sampling and analyzing of interstitial fluid or wholeblood samples which is suitable for hospital bedside and home use.

BACKGROUND OF THE INVENTION

[0003] The management of many medical conditions requires themeasurement and monitoring of a variety of analytes in bodily fluid.Historically, the measurement of analytes in blood has required aninvasive technique, such as a venipuncture or finger puncture, to obtainblood for sampling purposes. An example of an analyte which is routinelytested by obtaining a blood sample through an invasive technique isglucose. In order to control their condition, diabetics must monitortheir glucose levels on a regular basis. Invasive techniques used toobtain a blood sample for analysis have the disadvantage of beingpainful, which can reduce patient compliance in regular monitoring.Repeated testing, e.g., on a fingertip, can result in scar tissuebuild-up which makes obtaining a sample in that region more difficult.Moreover, invasive sampling procedures pose a risk of infection ordisease transmission.

[0004] An alternative is to sample interstitial fluid rather than wholeblood. Interstitial fluid is the fluid that fills the space between theconnective tissue and cells of the dermal layer of the skin. Anapplication where interstitial fluid has been shown to be an appropriatesampling substitute for plasma or whole blood is in the measurement ofglucose concentration (J. Lab. Clin. Med. 1997, 130, 436-41).

[0005] In the patents U.S. Pat. No. 5,879,367, U.S. Pat. No. 5,879,310,U.S. Pat. No. 5,820,570 and U.S. Pat. No. 5,582,184 are disclosedmethods of sampling using a fine needle in conjunction with a device tolimit the penetration depth to obtain small volumes of interstitialfluid for the purpose of glucose monitoring. However, there is no methoddisclosed for analyzing the drawn samples that is suitable for home useor hospital bedside use.

SUMMARY OF THE INVENTION

[0006] It is desirable to be able to measure the concentration ofanalytes in humans or other animals without having to draw a bloodsample by conventional methods. It is further desirable to be able to doso with an inexpensive disposable device that is simple enough for homeor hospital bedside use.

[0007] The invention provides a suitable alternative to conventionalsampling devices and methods that is less invasive than traditionalwhole blood sampling techniques and that requires a considerably smallersample volume than is required in the conventional venipuncture orfinger puncture sampling methods. Because of the smaller sample volumerequired, a smaller wound is necessary to obtain the sample. In theconventional finger stick method, a drop of blood is formed on the tipof a finger, then the sensor sample entrance is wetted with the drop.Because the sample comes into contact with the skin surface,contamination of the sample by material on the skin surface is possible.The devices and methods disclosed herein do not require forming a blooddrop on the surface of the skin, and therefore have less risk of samplecontamination.

[0008] In one embodiment of the present invention, a fluid samplingdevice is provided which includes a body, the body including a dermallayer penetration probe having a penetrating end and a communicatingend, and an analysis chamber having a proximal and distal end, theanalysis chamber having a volume, wherein the penetration probe is influid communication with the analysis chamber such that fluid can flowfrom the penetration probe toward the analysis chamber. The analysischamber can have at least one flexible wall which can be compressed toreduce the volume of the analysis chamber. The penetration probe caninclude, for example, a needle, a lancet, a tube, a channel, or a solidprotrusion and can be constructed of a material such as carbon fiber,boron fiber, plastic, metal, glass, ceramic, a composite material,mixtures thereof, and combinations thereof. The penetration probe caninclude two sheets of material in substantial registration, having aprotrusion on each sheet, wherein the sheets are spaced apart such thatliquid can be drawn between the sheets by capillary action. The twosheets of material can extend into the device so as to form apre-chamber. The penetration probe can be positioned within a recess inthe proximal end of the device, and the recess can be configured tosubstantially align with a shape of a selected dermal surface.

[0009] In a further embodiment, the device can further include apre-chamber having a volume and a first and second end, wherein thepre-chamber is interposed between the penetration probe and the analysischamber such that the first end of the pre-chamber is adjacent thecommunicating end of the penetration probe and the second end of thepre-chamber is adjacent the proximal end of the analysis chamber. Thevolume of the pre-chamber can be greater than or equal to the volume ofthe analysis chamber. The pre-chamber can have at least one flexiblewall that can be compressed to reduce the volume of the pre-chamber. Thepre-chamber can also include a valve at the first end capable ofsubstantially sealing the pre-chamber from the penetration probe.

[0010] In another embodiment, the device further includes a compressiblebladder in communication with the analysis chamber, the compressiblebladder being capable of applying a positive or a negative pressure tothe analysis chamber.

[0011] In yet another embodiment, the pre-chamber and the analysischamber can be capable of exerting different capillary forces. Thecapillary force exerted by the analysis chamber can be greater than thecapillary force exerted by the pre-chamber. The differential capillaryforce can be derived, at least in part, from a difference between thepre-chamber height and the analysis chamber height. In this embodiment,the interior surface of the pre-chamber can include at least first andsecond pre-chamber walls spaced apart at a first distance to define apre-chamber height, and the interior surface of the analysis chamber caninclude at least first and second analysis chamber walls spaced apart ata second distance to define an analysis chamber height, wherein theheight of the analysis chamber is less than the height of thepre-chamber.

[0012] In yet another further embodiment, at least one of the chamberscan include a substance capable of enhancing or diminishing thecapillary force exerted by the chamber. The substance can include, forexample, a polymer, a resin, a powder, a mesh, a fibrous material, acrystalline material, or a porous material. Suitable substances includepolyethylene glycol, polyvinylpyrrolidone, a surfactant, a hydrophilicblock copolymer, and polyvinylacetate.

[0013] In a further embodiment, the device further includes a releasableactuator capable of supplying a force sufficient to cause thepenetration probe to penetrate a dermal layer. The actuator can beexternal to or integral with the body, and upon release propels the bodytoward the dermal layer.

[0014] In a further embodiment, the analysis chamber can include anelectrochemical cell including a working electrode and acounter/reference electrode and an interface for communication with ameter, wherein the interface communicates a voltage or a current.

[0015] In yet another embodiment of the present invention, a method fordetermining a presence or an absence of an analyte in a fluid sample isprovided including the steps of providing a fluid sampling device asdescribed above; penetrating a dermal layer with the penetration probe;substantially filling the analysis chamber with a fluid sample byallowing the sample to flow from the penetration probe toward theanalysis chamber; and detecting a presence or an absence of the analytewithin the analysis chamber. The sample can include, for example,interstitial fluid and whole blood. A qualitative or quantitativemeasurement of a characteristic of the sample can be obtained in thedetecting step. The characteristic of the sample can include, forexample, a reaction product of the analyte, such as a color indicator,an electric current, an electric potential, an acid, a base, a reducedspecies, a precipitate, and a gas. The analyte can include, for example,an ion such as potassium, an element, a sugar, an alcohol such asethanol, a hormone, a protein, an enzyme, a cofactor, a nucleic acidsequence, a lipid, a pharmaceutical, and a drug. Cholesterol and lactateare examples of substances that can be analyzed.

[0016] In a further embodiment, the flow of sample toward the analysischamber can be driven by a driving force, e.g., capillary force or apressure differential. Where the analysis chamber has a flexible wall,the wall can be compressed to reduce the volume of the analysis chamberprior to penetrating the dermal, then the compression released to form apartial vacuum in the analysis chamber. Where the fluid sampling devicefurther includes a compressible bladder, the bladder can be compressedto reduce its volume, then after penetration of the dermal layer thecompression can be released to form a partial vacuum in the compressiblebladder and analysis chamber.

BRIEF DESCRIPTION OF THE DRAWINGS

[0017]FIG. 1 shows a top view (not to scale) of one embodiment of asampling device illustrating an arrangement of the penetration probe,pre-chamber, and analysis chamber.

[0018]FIG. 2 shows a cross section (not to scale) along the line A-A′ ofFIG. 1.

[0019]FIG. 3 shows a top view (not to scale) of one embodiment of asampling device illustrating an arrangement of the penetration probe,pre-chamber, and analysis chamber wherein the proximal edge of thedevice forms a recess.

[0020]FIG. 4 shows a top view (not to scale) of one embodiment of asampling device illustrating an arrangement of the penetration probe,pre-chamber, and analysis chamber.

[0021]FIG. 5 shows a cross section (not to scale) along the line B-B′ ofFIG. 4.

[0022]FIGS. 6a and 6 b (not to scale) depict an embodiment of theinvention wherein the device is loaded in a releasable actuator tofacilitate penetration of a dermal layer by the penetration probe. FIG.6a depicts the device loaded in the actuator, wherein the actuator is inthe cocked position, ready to be triggered. FIG. 6b depicts the deviceand actuator after triggering.

[0023]FIG. 7 is a schematic drawing (not to scale) of a first embodimentaccording to the invention shown in side elevation.

[0024]FIG. 8 shows the embodiment of FIG. 7 in plan, viewed from above.

[0025]FIG. 9 shows the embodiment of FIG. 7 in plan, viewed from below.

[0026]FIG. 10 shows the embodiment of FIG. 7 viewed in end elevation.

[0027]FIG. 11 is a schematic drawing (not to scale) of a secondembodiment according to the invention in side elevation.

[0028]FIG. 12 shows the embodiment of FIG. 11 in plan, viewed fromabove.

[0029]FIG. 13 is a schematic drawing (not to scale) of a thirdembodiment according to the invention, in side elevation.

[0030]FIG. 14 shows the embodiment of FIG. 13 in plan, viewed fromabove.

[0031]FIG. 15 is a schematic drawing (not to scale) according to theinvention in plan view, viewed from above.

[0032]FIG. 16 shows the embodiment of FIG. 15 in end elevation.

[0033]FIG. 17 shows the embodiment of FIG. 15 in side elevation.

[0034]FIG. 18 shows a schematic drawing (not to scale) of a hollow cellembodiment according to the invention, viewed in cross section.

[0035]FIG. 19 is a graph showing a plot of current (ordinate axis)versus time (co-ordinate axis) during conduct of a method according tothe invention.

[0036]FIG. 20 is a further graph of use in explaining the method of theinvention.

[0037] In FIGS. 11 to 12, components corresponding in function tocomponents of the embodiment of FIGS. 7 to 10 are identified byidentical numerals or indicia.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0038] Introduction

[0039] The following description and examples illustrate variousembodiments of the present invention in detail. Those of skill in theart will recognize that there are numerous variations and modificationsof this invention that are encompassed by its scope. Accordingly, thedescription of a preferred embodiment should not be deemed to limit thescope of the present invention. Methods and devices for optimizingsampling of fluid samples are discussed further in copending U.S. patentapplication Ser. No. 09/536,234, filed on Mar. 27, 2000, entitled“METHOD OF PREVENTING SHORT SAMPLING OF A CAPILLARY OR WICKING FILLDEVICE,” which is incorporated herein by reference in its entirety.

[0040] The invention disclosed in this application is a method anddevice for combining the sampling and analyzing of a fluid sample fromsub-dermal tissue in a device suitable for hospital bedside and homeuse. The fluid sample can comprise, but is not limited to, interstitialfluid or whole blood samples obtained from an animal. Any fluid sampleobtained from sub-dermal tissue of a plant or an animal can sampled andanalyzed, thus the invention has broad application in the fields ofhuman medicine, veterinary medicine, and horticultural science. Thedevice and method are applicable to any analyte that exists in ausefully representative concentration in the fluid sample. For clarity,the present disclosure will discuss the application to glucosemonitoring. However, it is to be understood that the invention is notlimited to the monitoring of glucose, and that other analytes, asdiscussed below, can also be measured.

[0041] The method utilizes an integrated sampling and analyzing device10 incorporating a penetration probe 12 capable of penetrating apatient's dermal layers to extract an interstitial fluid or whole bloodsample, and a method for transferring the sample from the penetrationprobe 12 to the analysis chamber 20. In one embodiment, the device 12can be a one-shot disposable device which can be inserted into a meterwhich communicates with the analysis chamber 20 to perform the analysisof the sample and present and optionally store the result.

[0042] In the device 10, a penetration probe 12 for penetrating thesubject's dermal layers to collect an interstitial fluid or whole bloodsample is integrated with an analysis chamber 20. A property of samplinginterstitial fluid is that it can take from several to tens of secondsto collect sufficient sample to analyze. This is often not desirable foran analysis chamber 20 wherein the analyte undergoes a reaction as partof the analysis process, as it can be difficult to obtain an accuratestart time for the test as well as achieve an even reacting reagentdistribution in the sample. In a second aspect of the current inventiona method is disclosed for collecting the sample in a pre-chamber 14 and,when full, transferring the sample quickly to an analysis chamber 20.

[0043] In this disclosure, unless a different meaning is clear from thecontext of its usage, “proximal” refers to a region or structure of thedevice situated toward or adjacent to the dermal surface to bepenetrated, and “distal” refers a region or structure of the devicesituated toward the opposite (non-proximal) end of the device. Forexample, the penetration probe 12 is at the proximal end of the device.

[0044] The Penetration Probe

[0045] The penetration probe 12 can be any device capable of penetratingthe patient's dermal layers to the desired extent and capable oftransporting a sample to a pre-chamber 14 or analysis chamber 20. Thepenetration probe 12 comprises two ends, as illustrated in FIG. 1. Thepenetrating end 11 of the penetration probe 12 is the end inserted intothe dermal layer. The communicating end 13 of the penetration probe 12is the end which is in communication with either the pre-chamber 14 orthe analysis chamber 20.

[0046] One or more protrusions 12 with at least one sharp edge or pointare suitable as the penetration probe 12. The penetration probe 12 canbe fabricated from materials including plastic, metal, glass, ceramic, acomposite material (e.g., a composite of ceramic and metal particles),or mixtures and combinations of these materials. The penetration probe12 can be in the form of a solid protrusion, a needle, a lancet, a tubeor a channel. The channel can optionally be open along one or more ofits elongated sides. As illustrated in FIG. 2, a preferred embodiment ofthe penetration probe 12 is two sheets 30 of material formed so as tohave a sharply pointed protrusion 12 on each sheet 30 in substantialregistration, with the sheets 30 spaced apart such that liquid can bedrawn between the sheets 30 by capillary action. In a particularlypreferred embodiment, the two sheets 30 of material extend to andoverlap with the analysis chamber 20 to form a pre-chamber 14 for samplecollection.

[0047] When interstitial fluid is sampled, the penetration depth can becontrolled by limiting the length the penetration probe 12 protrudesfrom the proximal surface 34 of the sampling device 10 to less than thethickness of the dermal layer. In a preferred embodiment, the length ofthe protrusion 12 will be less than 2 to 3 mm, more preferably about 1.5mm. After penetration to a suitable depth corresponding to the length ofthe protrusion 12, contact between the surface of the dermal layer andthe surface 34 of the analyzing device prevents further penetration. Forother uses, such as in sampling interstitial fluid from regions having athick dermal layer, or for veterinary uses, it can be desirable for thelength of the protrusion 12 to be greater than 3 mm. Accordingly, theinvention contemplates protrusions 12 of any length, wherein the lengthis sufficient to sample interstitial fluid. When whole blood is sampled,a slightly longer penetration probe 12 should be used, i.e., one havinga length greater than 2 to 3 mm.

[0048] The diameter or width of the penetration probe 12 depends uponthe design of the penetration probe 12. Suitable diameters or widths arethose which provide sufficient sample flow. In the case of a protrusion12 forming a sharp edge or point, or a tube or channel, the minimumdiameter or width is typically greater than about 10 μm. When thepenetrating means 12 comprises two sheets 30 in substantialregistration, each having a sharply pointed protrusion 12, the twoprotrusions 12 are typically spaced from 1 mm to 10 μm apart.

[0049] The penetration probe 12 can be located on any suitable part ofthe test strip 10, i.e., an edge 34, a corner 42, or one of the flatsurfaces 44. Protection can be provided to the penetration probe 12 bylocating it within a recess formed in the distal edge 34 of the teststrip 10, as shown in FIG. 3, or in a depression on the surface 44 ofthe test strip 10. In a preferred embodiment, the recess in the distaledge 34 of the test strip 10 can be configured to substantially alignwith the shape of a selected dermal surface, e.g., a fingertip. However,the recess can be configured in other suitable shapes, e.g., a squarerecess, a V-shaped recess, a curved recess, a polygonal recess, and thelike. In a preferred embodiment, the penetration probe 12 does notprotrude past the proximal-most portion of the proximal edge 34 orsurface 44 of the device 10, but when pressed against the skin, the skindeforms into the recess and is punctured by the penetration probe 12.Such an arrangement aids sampling by compressing the area of the skinaround the sampling point. The penetration probe 12 can form an integralpart of another component of the test strip 10, e.g., a side of thepre-chamber 54, as shown in FIG. 2. Alternatively, the penetration probe12 can comprise a separate part which is attached to or incorporatedinto the test strip 10 by any suitable means, e.g., adhesive, thermalbonding, interlocking parts, pressure, and the like. The penetrationprobe 12 can be retractable or non-retractable.

[0050] Penetration itself can be accomplished by any suitable means,including inserting the penetration device 12 manually or by means of areleasable actuator 84 such as, for example, a spring-loaded mechanism84 as depicted in FIGS. 6a and 6 b. Such a spring-loaded mechanism 84incorporates a spring 86 which is compressed and held in place by atrigger 88 which can release the force compressing the spring 86 whenthe triggering mechanism is activated. The trigger 88 can be activatedmanually, or the device 84 can incorporate a pressure sensor whichindicates that sufficient pressure has been applied to obtain thesample, thereby activating the trigger 88. In one embodiment, the distalend of the device 10 is placed in the spring-loaded mechanism 84 suchthat when the force compressing the spring 86 is released by activatingthe trigger 88, force is transferred to the device 10, which is ejectedfrom the mechanism 84, thereby inserting the penetrating probe 12 intothe dermal layer.

[0051] Any suitable body part can be used for sampling. In a preferredembodiment, the sampling area is one which does not have a high densityof nerve endings, e.g., the forearm. Typically, 5 to 15 seconds isrequired to obtain sufficient sample. Application of pressure to thesampling area can be needed to extract interstitial fluid or wholeblood. To facilitate the appropriate amount of pressure being applied, apressure sensor can be incorporated into the device 10 which indicateswhen sufficient pressure has been applied. Sample acquisition time canbe improved by applying increased pressure to the area surrounding thedirect sampling area. Some of the factors that can affect interstitialfluid or whole blood sample acquisition include the patient's age, skinthickness, temperature, and hydration. The amount of interstitial orwhole blood sample collected for testing can preferably be about 0.02 μlor greater, more preferably 0.1 μl or greater, and most preferably about0.5 μl or greater.

[0052] In one preferred embodiment, the device 10 can be inserted into ameter prior to sample acquisition. In such an embodiment, the meterserves multiple functions, including supporting the device 10, providingan automated means of initiating sample acquisition, and indicating whensample acquisition is complete.

[0053] Transfer of Sample from Penetration probe to Analysis Chamber

[0054] In a preferred embodiment of the sampling device 10, the devicecomprises two parts—the penetration probe 12 and an analysis chamber 20.In another preferred embodiment, illustrated in FIGS. 1 and 2, thedevice 10 comprises the penetration probe 12 and a pre-chamber 14. Thepre-chamber 14 can then be integrated with or can be interfaced to theanalysis chamber 20.

[0055] In a further embodiment, the analysis chamber 20 is integratedwith or can be interfaced to a means for facilitating filling of theanalysis chamber 20. This means can comprise a collapsible orcompressible bladder 22, as shown in FIGS. 3 and 4, which can be used toapply a positive or negative pressure (i.e., partial vacuum) to theanalysis chamber 20. The compressible bladder 22 can comprise anychamber with flexible walls that can be compressed to reduce the volumeof the chamber. When the force compressing the compressible bladder 22is released, a partial vacuum is formed which draws sample into theanalysis chamber 20. In a preferred embodiment, the volume of thecompressible bladder 22 is sufficiently large so that when the bladder22 is substantially fully compressed, the reduction in volume of thebladder 22 is larger than or equal to the total volume of the analysischamber 20, thereby ensuring that the analysis chamber 20 issubstantially filled. However, a compressible bladder 22 with a smallervolume than the analysis chamber 20 can also be effective in assistingthe filling of the analysis chamber 20.

[0056] Alternatively, the analysis chamber 20 itself can be collapsibleor compressible. In such an embodiment, a piston or other compressingagent, such as a patient's or clinician's fingers, can first compressthen release the analysis chamber 20, thereby forming a partial vacuum.When the compressing force is released, the partial vacuum causes thesample to flow from the penetration probe toward the analysis chamber.

[0057] Pre-chamber

[0058] In a preferred embodiment, as illustrated in FIGS. 1 and 2, apre-chamber 14 is provided in the integrated sampling and testing device10 for accumulation and storage of the collected sample prior to itsbeing transferred to the analysis chamber 20. A pre-chamber 14 is usefulwhen using an analysis method which requires that the sample fill theanalysis chamber 20 in a short period of time to return accurateresults, i.e., a time shorter than that required to draw sufficientsample from the dermal layer. In a preferred embodiment, the volume ofthe pre-chamber 14 is larger than that of the analysis chamber 20, thusensuring that once the pre-chamber 14 is filled, sufficient sample hasbeen collected to completely fill the analysis chamber 20.

[0059] In a preferred embodiment, as illustrated in FIGS. 1 and 2, thepenetration probe 12 opens into the pre-chamber 14 at a first end, andat the second end the pre-chamber 14 opens to the analysis chamber 20.The pre-chamber 14 can be free of reagents or other substances, or canoptionally contain one or more substances to enhance or diminish thecapillary force exerted by the walls of the pre-chamber 14 or topre-treat the sample prior to analysis. These substances can include,for example, polymers, resins, powders, meshes, fibrous materials,crystalline materials, porous materials, or a mixture or combinationthereof. To facilitate effective filling of the analysis chamber 20, apreferred embodiment utilizes a pre-chamber 14 and analysis chamber 20of different heights, as shown in FIG. 2. Where the analysis chamber 20is formed so that its height (typically referring to the smallestchamber dimension) is smaller than the height of the pre-chamber 14, acapillary force is generated that is capable of drawing fluid out of thepre-chamber 14 and into the analysis chamber 20. A first air vent 64 canbe formed at the end 70 of the analysis chamber 20 opposite the opening62 to the pre-chamber 14, facilitating the filling of the analysischamber 20 by allowing air to be displaced from the analysis chamber 20as sample enters. Optionally, a second vent 74 can be formed openinginto the pre-chamber 14 at the substantially opposite end 60 of thepre-chamber 14 to where the penetration probe 12 opens into thepre-chamber 14. This vent 74 provides air to the pre-chamber 14 toreplace the sample as it is transferred from the pre-chamber 14 to theanalysis chamber 20. The vent 74 can be placed in any suitable positionon the test strip 10. In a preferred embodiment, the vent 74incorporates a sharp corner, e.g., at a 90° angle, which functions as a“capillary stop” to prevent sample from exiting the device 10 throughthe vent 74.

[0060] In another embodiment, the pre-chamber 14 consists of a tube, orother shaped chamber, with flexible walls, attached to the penetrationprobe 12. In this embodiment, the pre-chamber 14 is either permanentlyfixed to the analysis chamber 20 or is placed next to and aligned with aport to the analysis chamber 20. Such alignment can occur during use bysuitable placement in an external device such as the measurement meter.

[0061] In one aspect of this embodiment, the pre-chamber 14 furthercomprises a valve, defined as a device to control the flow of fluidsample between the penetration probe 12 and the pre-chamber 14. Thevalve can comprise one or more rollers, pistons, or squeezing devicescapable of simultaneously closing off the first end 60 of thepre-chamber 14, and compressing the pre-chamber 14 such that the fluidin the pre-chamber 14 is forced towards the second end 62 of thepre-chamber 14 and subsequently into the analysis chamber 20.

[0062] Alternatively, the analysis chamber 20 consists of a tube, orother shaped chamber, with flexible walls, attached to the penetrationprobe 12. In one aspect of this embodiment, the analysis chamber 20,prior to penetration, is compressed by one or more rollers, pistons, orother squeezing devices. After the penetration probe 12 is inserted, thecompression is released, forming a vacuum which pulls sample into theanalysis chamber 20. In such an embodiment, the pre-chamber 14 can notbe necessary if sufficient vacuum is generated for rapid sampleacquisition. In such an embodiment, the device 10 can not require a vent64, 74 if such would interfere with forming a vacuum.

[0063] In another embodiment, illustrated in FIGS. 3 and 4, apre-chamber 14 of suitable size is formed which opens to the penetrationprobe 12 on one end 60 and to the analysis chamber 20 on the other end62. The end 70 of the analysis chamber 20 opposite to that opening tothe pre-chamber 14 opens to a compressible bladder 22. The bladder 22can be formed separately and attached to the end 70 of the analysischamber 20. Alternatively, it can be formed by removing a section on themiddle laminate 82 in the test strip 10, similar to those described inWO97/00441 (incorporated herein by reference in its entirety), asillustrated in FIGS. 3 and 4.

[0064] In use, the bladder 22 in the strip 10 is compressed by suitablemeans prior to the penetration probe 12 being inserted into the patient.Insertion of the penetration probe 12 can be confirmed by use of asensor, such as a pressure sensor, or the patient can confirm that thepenetration probe 12 is inserted either visually or by touch. In thelatter case, the patient sensing can signal the meter, such as bypushing a button. At this point, the means compressing the bladder 22 iswithdrawn to a halfway position to draw sample into the pre-chamber 14.When the pre-chamber 14 is full, as indicated by a suitable sensor, themeter indicates to the patient to withdraw the penetration probe 12. Thecompressing means then moves to its fully withdrawn position and sodraws the sample from the pre-chamber 14 into the analysis chamber 20.In the case where the initial suction from the bladder 22 causes thesample to be accumulated with sufficient speed, the pre-chamber 14 canbe dispensed with and the bladder 22 used to draw sample through thepenetration probe 12 directly into the analysis chamber 20. A vent 64,74 which would interfere with forming a vacuum need not be incorporatedinto the device in some embodiments.

[0065] Analysis Chamber

[0066] In a preferred embodiment, the analysis chamber 20 is containedin an analyzing device 10 comprising a disposable analysis strip similarto that disclosed in WO97/00441. The analysis strip of WO97/00441contains a biosensor for determining the concentration of an analyte ina carrier, e.g., the concentration of glucose in a fluid sample. Theelectrochemical analysis cell 20 in this strip has an effective volumeof 1.5 μl or less, and can comprise a porous membrane, a workingelectrode on one side of the membrane, and a counter/reference electrodeon the other side. In a preferred embodiment, an analysis cell 20 havingan effective volume of about 0.02 μl or greater is used. Morepreferably, the cell 20 has a volume ranging from about 0.1 μl to about0.5 μl.

[0067] In one aspect of this embodiment, the penetration probe 12 is asmall needle integrated into the analysis strip 10 by being insertedthrough a wall of the analysis chamber 20 such that one end of theneedle 12 opens into the strip analysis chamber 20. In using a device 10having this arrangement to obtain and analyze a sample of interstitialfluid, the needle 12 is inserted into the patient's dermal layer andsample is drawn into the needle 12 via capillary action. The sample isthen transferred from the needle 12 into the analysis chamber 20 bycapillary action whereupon the sample is analyzed. An opening 64 in theanalysis chamber 20 to atmosphere, remote from the point where theneedle 12 opens into the chamber, acts as a vent 64 to allow the escapeof displaced air as the analysis chamber 20 fills with sample. Analysisdevices of the type disclosed in WO97/00441 are particularly suited foruse with this arrangement because of their ability to utilize the verysmall volumes of sample typically available with interstitial fluidsampling.

[0068] The analysis chamber 20 can contain one or more substances toenhance or diminish the capillary force exerted by the walls of analysischamber 20. Such materials can include polymers, resins, powders,meshes, fibrous materials, crystalline materials, porous materials, or amixture or combination thereof, as can also be used in the pre-chamber,discussed above. For example, the walls 24 of the analysis chamber 20can be coated with a hydrophilic material to encourage the flow of fluidsample into the analysis chamber. Suitable hydrophilic materials includepolyethylene glycol, polyvinylpyrrolidone, a surfactant, a hydrophilicblock copolymer, and polyacrylic acid. The analysis chamber 20 can alsocontain reagents capable of reacting with the analyte or othersubstances present in the sample. Such other substances can includesubstances which interfere in determining the presence or absence of theanalyte. In such cases, the reagent will react with the substance sothat it no longer interferes with the analysis.

[0069] Any analyte present in a fluid sample in a detectable amount canbe analyzed using the device 10. A typical analytes can include, but isnot limited to, an ion, an element, a sugar, an alcohol, a hormone, aprotein, an enzyme, a cofactor, a nucleic acid sequence, a lipid, and adrug. In a preferred embodiment, glucose is the analyte to be tested.Typical analytes could include, but are not limited to, ethanol,potassium ion, pharmaceuticals, drugs, cholesterol, and lactate.

[0070] The presence or absence of the analyte can be determineddirectly. Alternatively, the analyte can be determined by reacting theanalyte with one or more reagents present in the analysis chamber. Theproduct of that reaction, indicative of the presence or absence of theanalyte, would then be detected. Suitable reaction products include, butare not limited to, a color indicator, an electric current, an electricpotential, an acid, a base, a precipitate, or a gas.

[0071] Any suitable analytical method can be used for determining thepresence or absence of the analyte or a reaction product of the analyte.Suitable analytical methods include, but are not limited to,electrochemical methods, photoabsorption detection methods,photoemission detection methods, and the measurement of magneticsusceptibility. In the case of a reaction product having a differentcolor than the analyte, or the formation of a precipitate or a gas, avisual determination can be a suitable method for determining thepresence or absence of the analyte.

[0072] With reference to FIGS. 7 to 10 there is shown a first embodimentof apparatus of the invention, in this case a biosensor for determiningglucose in blood. The embodiment comprises a thin strip membrane 1having upper and lower surfaces 2, 3 and having a cell zone 4 definedbetween a working electrode 5 disposed on upper surface 2 and a counterelectrode 6 disposed on lower surface 3. The membrane thickness isselected so that the electrodes are separated by a distance “I” which issufficiently close that the products of electrochemical reaction at thecounter electrode migrate to the working electrode during the time ofthe test and a steady state diffusion profile is substantially achieved.Typically, “I” will be less than 500 μm. A sample deposition or “target”area 7 defined on upper surface 2 of membrane 1 is spaced at a distancegreater than the membrane thickness from cell zone 4. Membrane 1 has adiffusion zone 8 extending between target area 7 and cell zone 4. Asuitable reagent including a redox mediator “M”, an enzyme “E” and a pHbuffer “B” are contained within cell zone 4 of the membrane and/orbetween cell zone 4 and target area 7. The reagent may also includestabilisers and the like.

[0073] In some cases it is preferable to locate the enzyme and mediatorand/or the buffer in different zones of the membrane. For example themediator may be initially located within electrochemical cell zone 4while the enzyme may be situated below target area 7 or in diffusionzone 8.

[0074] Haemoglobin releases oxygen at low pH's, but at higher pH's itbinds oxygen very firmly. Oxygen acts as a redox mediator for glucoseoxidase dehydroienase (GOD). In a glucose sensor this competes with theredox mediator leading to low estimates of glucose concentration.Therefore if desired a first pH buffer can be contained in the vicinityof target area 7 to raise the pH to such a level that all the oxygen isbound to haemoglobin. Such a pH would be non-optimal for GOD/glucosekinetics and would consequently be detrimental to the speed andsensitivity of the test.

[0075] In a preferred embodiment of the invention a second pH buffer iscontained as a reagent in the vicinity of the working electrode torestore the pH to kinetically optimal levels.

[0076] The use of a second buffer does not cause oxygen to be releasedfrom the haemoglobin as the haemoglobin is contained within the bloodcells which are retained near blood target area 7 or are retarded indiffusion in comparison with the plasma and therefore not influenced bythe second buffer. In this manner oxygen interference may be greatlyreduced or eliminated.

[0077] In use of the sensor a drop of blood containing a concentrationof glucose to be determined is placed on target zone 7. The bloodcomponents wick towards cell zone 4, the plasma component diffusing morerapidly than red blood cells so that a plasma front reaches cell zone 4in advance of blood cells.

[0078] When the plasma wicks into contact with the reagent, the reagentis dissolved and a reaction occurs that oxidises the analyte and reducesthe mediator. After allowing a predetermined time to complete thisreaction an electric potential difference is applied between the workingelectrode and the counter electrode. The potential of the workingelectrode is kept sufficiently anodic such that the rate ofelectrooxidation of the reduced form of the mediator at the workingelectrode is determined by the rate of diffusion of the reduced form ofthe mediator to the working electrode, and not by the rate of electrontransfer across the electrode/solution interface.

[0079] In addition the concentration of the oxidised form of themediator at the counter electrode is maintained at a level sufficient toensure that when a current flows in the electrochemical cell thepotential of the counter electrode, and thus also the potential of theworking electrode, is not shifted so far in the cathodic direction thatthe potential of the working electrode is no longer in the diffusioncontrolled region. That is to say, the concentration of the oxidizedform at the counter electrode must be sufficient to maintain diffusioncontrolled electrooxidation of the reduced form of the mediator at theworking electrode.

[0080] The behavior of a thin layer cell is such that if both oxidisedand reduced forms of the redox couple are present, eventually a steadystate concentration profile is established across the cell. This resultsin a steady state current. It has been found that by comparing a measureof the steady state current with the rate at which the current varies inthe current transient before the steady state is achieved, the diffusioncoefficient of the redox mediator can be measured as well as itsconcentration.

[0081] More specifically, by solving the diffusion equations for thissituation it can be shown that over a restricted time range a plot ofln(i/i-1) vs. time (measured in seconds) is linear and has a slope(denoted by S) which is equal to −4π²D/1², where “i” is the current attime “t”, “V” is the steady state current, “D” is the diffusioncoefficient in cm²/sec, “1” is the distance between the electrodes in cmand “π” is approximately 3.14159. The concentration of reduced mediatorpresent when the potential was applied between the electrodes is givenby 2π²i /FA1S, where “T” is Faraday's constant, “A” is the workingelectrode area and the other symbols are as given above. As this laterformula uses S it includes the measured value of the diffusioncoefficient.

[0082] Since I is a constant for a given cell, measurement of i as afunction of time and i enable the value of the diffusion coefficient ofthe redox mediator to be calculated and the concentration of the analyteto be determined.

[0083] Moreover the determination of analyte concentration compensatesfor any variation to the diffusion coefficient of the species which iselectrooxidised or electroreduced at the working electrode. Changes inthe value of the diffusion coefficient may occur as a result of changesin the temperature and viscosity of the solution or variation of themembrane permeability. Other adjustments to the measured value of theconcentration may be necessary to account for other factors such aschanges to the cell geometry, changes to the enzyme chemistry or otherfactors which may effect the measured concentration. If the measurementis made on plasma substantially free of haematocrit (which if presentcauses variation in the diffusion coefficient of the redox mediator) theaccuracy of the method is further improved.

[0084] Each of electrodes 5, 6 has a predefined area. In the embodimentsof FIGS. 7 to 10 cell zone 4 is defined by edges 9, 10, 11 of themembrane which correspond with edges of electrodes 5, 6 and by leading(with respect to target area 7) edges 12, 13 of the electrodes. In thepresent example the electrodes are about 600 angstrom thick and are from1 to 5 mm wide.

[0085] Optionally, both sides of the membrane are covered with theexception of the target area 7 by laminating layers 14 (omitted fromplan views) which serves to prevent evaporation of water from the sampleand to provide mechanical robustness to the apparatus. Evaporation ofwater is undesirable as it concentrates the sample, allows theelectrodes to dry out, and allows the solution to cool, affecting thediffusion coefficient and slowing the enzyme kinetics, althoughdiffusion coefficient can be estimated as above.

[0086] A second embodiment according to the invention, shown in FIGS. 11and 12, differs from the first embodiment by inclusion of a secondworking electrode 25 and counter/reference electrode 26 defining asecond cell zone 24 therebetween. These electrodes are also spaced apartby less than 500 μm in the present example. Second electrodes 25, 26 aresituated intermediate cell zone 4 and target area 7. In this embodimentthe redox mediator is contained in the membrane below or adjacent totarget area 7 or intermediate target area 7 and first cell zone 4. Theenzyme is contained in the membrane in the first cell zone 4 and secondcell zone 24. The enzyme does not extend into second cell 24. In thiscase when blood is added to the target area, it dissolves the redoxmediator. This wicks along the membrane so that second electrochemicalcell 24 contains redox mediator analyte and serum includingelectrochemically interfering substances. First electrochemical cellreceives mediator, analyte, serum containing electrochemicallyinterfering substances, and enzyme.

[0087] Potential is now applied between both working electrodes and thecounter electrode or electrodes but the change in current with time ismeasured separately for each pair. This allows the determination of theconcentration of reduced mediator in the absence of analyte plus theconcentration of electrochemically interfering substances in the secondelectrochemical cell and the concentration of these plus analyte in thefirst electrochemical cell. Subtraction of the one value from the othergives the absolute concentration of analyte.

[0088] The same benefit is achieved by a different geometry in theembodiment of FIGS. 13 and 14 in which the second working electrode andsecond counter/reference electrode define the second cell 24 on the sideof target area 7 remote from first electrochemical cell 4. In this casethe enzyme may be contained in the membrane strip between the targetarea and cell 1. The redox mediator may be in the vicinity of the targetarea or between the target area and each cell. The diffusion coefficientof mediator is lowered by undissolved enzyme and the arrangement ofFIGS. 13 and 14 has the advantage of keeping enzyme out of the thinlayer cells and allowing a faster test (as the steady state current isreached more quickly). Furthermore the diffusion constant of redoxmediator is then the same in both thin layer cells allowing moreaccurate subtraction of interference.

[0089] Although the embodiments of FIGS. 7 to 14 are unitary sensors, itwill be understood that a plurality of sensors may be formed on a singlemembrane as shown in the embodiment of FIGS. 15 to 17. In this case theelectrodes of one sensor are conductively connected to those of anadjacent sensor. Sensors may be used successively and severed from thestrip after use.

[0090] In the embodiment of FIGS. 15 to 17 electrode dimensions aredefined in the diffusion direction (indicated by arrow) by the width ofthe electrode in that direction.

[0091] The effective dimension of the electrode in a directiontransverse to diffusion direction is defined between compressed volumes16 of the membrane in a manner more fully described in co-pendingApplication PCT/AU96/00210. For clarity optional laminated layer 14 ofFIG. 7 has been omitted from FIGS. 15 to 17.

[0092] In the embodiment of FIG. 18 there is shown a hollow cellaccording to the invention wherein the electrodes 5, 6 are supported byspaced apart polymer walls 30 to define a hollow cell. An opening 31 isprovided on one side of the cell whereby a sample can be admitted intocavity 32. In this embodiment a membrane is not used. As in previousembodiments, the electrodes are spaced apart by less than 500 μm,preferably 20-400 μm and more preferably 20-200 μm. Desirably theeffective cell volume is 1.5 microlitres or less.

[0093] It will be understood that the method of the invention may beperformed with a cell constructed in accord with co-pending applicationPCT/AU95/00207 or cells of other known design, provided these aremodified to provide a sufficiently small distance between electrodefaces.

[0094] The method of the invention will now be further exemplified withreference to FIGS. 19 and 20.

[0095] A membrane 130 microns thick was coated on both sides with alayer of Platinum 60 nanometers thick. An area of 12.6 sq. mm wasdefined by compressing the membrane. 1.5 microlitres of a solutioncontaining 0.2 Molar potassium ferricyanide and 1% by weight glucoseoxidase dehydrotenase was added to the defined area of the membrane andthe water allowed to evaporate.

[0096] The platinum layers were then connected to a potentiostat to beused as the working and counter/reference electrodes. 3 microlitres ofan aqueous solution containing 5 millimolar D-glucose and 0.9 wt % NaClwas dropped on to the defined area of the membrane. After an elapse of20 seconds a voltage of 300 millivolts was applied between the workingand counter/reference electrodes and the current recorded for a further30 seconds at intervals of 0.1 seconds.

[0097]FIG. 19 is a graph of current versus time based on the abovemeasurements.

[0098] Using a value of the steady state current of 26.9 microamps thefunction ln(i/26.9-1) was computed and plotted versus time. The slope ofthe graph (FIG. 20) is −0.342 which corresponds to a diffusioncoefficient of 1.5×10⁶ cm² per second and a corrected glucoseconcentration (subtracting background ferrocyanide) of 5.0 millimolar.

[0099] The steady state current is one in which no further significantcurrent change occurs during the test. As will be understood by thoseskilled in the art, a minimum current may be reached after which theremay be a drift due to factors such as lateral diffusion, evaporation,interfering electrochemical reactions or the like. However, in practiceit is not difficult to estimate the “steady state” current (i). Onemethod for doing so involves approximating an initial value for i. Usingthe fit of the i versus t data to the theoretical curve a betterestimate of i is then obtained. This is repeated reiteratively until themeasured value and approximated value converge to within an acceptabledifference, thus yielding an estimated i.

[0100] In practice, the measurements of current i at time t are madebetween a minimum time t min and a maximum time t max after thepotential is applied. The minimum and maximum time are determined by theapplicability of the equations and can readily be determined byexperiment of a routine nature. If desired the test may be repeated byswitching off the voltage and allowing the concentration profiles of theredox species to return towards their initial states.

[0101] It is to be understood that the analysis of the current v. timecurve to obtain values of the Diffusion Coefficient and/or concentrationis not limited to the method given above but could also be achieved byother methods.

[0102] For instance, the early part of the current v. time curve couldbe analysed by the Cottrell equation to obtain a value of D^(1/2)×Co(Co=Concentration of analyte) and the steady state current analysed toobtain a value of D×Co. These two values can then be compared to obtainD and C separately.

[0103] It will be understood that in practice of the invention anelectrical signal is issued by the apparatus which is indicative ofchange in current with time. The signal may bean analogue or digitalsignal or may be a series of signals issued at predetermined timeintervals. These signals may be processed by means of a microprocessoror other conventional circuit to perform the required calculations inaccordance with stored algorithms to yield an output signal indicativeof the diffusion coefficient, analyte concentration, haematocritconcentration or the like respectively. One or more such output signalsmay be displayed by means of an analogue or digital display.

[0104] It is also possible by suitable cell design to operate the cellas a depletion cell measuring the current required to deplete themediator. For example in the embodiment of FIG. 5 the method of theinvention may be performed using electrodes 5, 6, which are spaced apartby less than 500 μm. An amperometric or voltammetric depletionmeasurement may be made using electrodes 5 and 26 which are spaced apartmore than 500 μm and such that there is no interference between theredox species being amperometrically determined at electrodes 5, 26.

[0105] The depletion measurement may be made prior to, during orsubsequent to, the measurement of diffusion coefficient by the method ofthe invention. This enables a substantial improvement in accuracy andreproducibility to be obtained.

[0106] In the embodiments described the membrane is preferably anasymmetric porous membrane of the kind described in Patent No. 4,629,563and 4,774,039. However symmetrical porous membranes may be employed. Themembrane may be in the form of a sheet, tube, hollow fibre or othersuitable form.

[0107] If the membrane is asymmetric the target area is preferably onthe more open side of the asymmetric membrane. The uncompressed membranedesirably has a thickness of from 20 to 500 μm. The minimum thickness isselected having regard to speed, sensitivity, accuracy and cost. Ifdesired a gel may be employed to separate haematocrit from GOD. The gelmay be present between the electrodes and/or in the space between thesample application area and the electrodes.

[0108] The working electrode is of any suitable metal for example gold,silver, platinum, palladium, iridium, lead, a suitable alloy. Theworking electrode may be preformed or formed in situ by any suitablemethod for example sputtering, evaporation under partial vacuum, byelectrodeless plating, electroplating, or the like. Suitable non-metalconductors may also be used for electrode construction. For example,conducting polymers such as poly(pyrrole), poly(aniline), porphyrin“wires”, poly(isoprene) and poly (cis-butadiene) doped with iodine and“ladder polymers”. Other non-metal electrodes may be graphite or carbonmixed with a binder, or a carbon filled plastic.

[0109] Inorganic electrodes such as In₂O₃ or SnO₂ may also be used. Thecounter/reference electrode may for example be of similar constructionto the working electrode. Nickel hydroxide or a silver halide may alsobe used to form the counter/reference electrode.

[0110] Silver chloride may be employed but it will be understood thatchloridisation may not be necessary and silver may be used if sufficientchloride ions are present in the blood sample. Although in theembodiments described the working electrode is shown on the uppersurface of the biosensor and the counter/reference electrode is on thelower surface, these may be reversed.

[0111] It is preferable that the working electrode and counter (orcounter/reference) electrodes are of substantially the same effectivegeometric area.

[0112] If a separate reference and counter electrode are employed, theymay be of similar construction. The reference electrode can be in anysuitable location.

[0113] It will be understood that the features of one embodiment hereindescribed may be combined with those of another. The invention is notlimited to use with any particular combination of enzyme and mediatorand combinations such as are described in EP0351892 or elsewhere may beemployed. The system may be used to determine analytes other thanglucose (for example, cholesterol) by suitable adaptation of reagentsand by appropriate membrane selection. The system may also be adaptedfor use with media other than blood. For example the method may beemployed to determine the concentration of contaminants such aschlorine, iron, lead, cadmium, copper, etc., in water.

[0114] Although the cells herein described have generally planar andparallel electrodes it will be understood that other configurations maybe employed, for example one electrode could be a rod or needle and theother a concentric sleeve.

[0115] Display/Storage of Measurement Data

[0116] In a preferred embodiment, an analysis strip as described aboveor another embodiment of the sampling device 10 is integrated with ameasuring device, e.g., a meter, which can display, store or record testdata, optionally in computer-readable format. In such an embodiment, thetest strip 10 comprises an interface for communicating with the meter,e.g., conductive leads from the electrodes of the electrochemical cell20. In the case of obtaining an electrochemical measurement, theinterface communicates a voltage or a current to the electrochemicalcell 20.

[0117] The above description discloses several methods and materials ofthe present invention. This invention is susceptible to modifications inthe methods and materials, as well as alterations in the fabricationmethods and equipment. Such modifications will become apparent to thoseskilled in the art from a consideration of this disclosure or practiceof the invention disclosed herein. Consequently, it is not intended thatthis invention be limited to the specific embodiments disclosed herein,but that it cover all modifications and alternatives coming within thetrue scope and spirit of the invention as embodied in the attachedclaims.

What is claimed is:
 1. A fluid sampling device, the device comprising abody, the body comprising: a dermal layer penetration probe having apenetrating end and a communicating end, the penetration probe having avolume; and an analysis chamber having a proximal end and a distal end,the analysis chamber having a volume, wherein the volume of thepenetration probe is greater than the volume of the analysis chamber,and wherein the penetration probe is in fluid communication with theanalysis chamber such that fluid can flow from the penetration probe tothe analysis chamber.
 2. The device of claim 1, wherein the penetrationprobe is capable of exerting a first capillary force and the analysischamber is capable of exerting a second capillary force, and wherein adifferential in capillary force exists between the first capillary forceand the second capillary force.
 3. The device of claim 2, wherein thesecond capillary force is greater than the first capillary force.
 4. Thedevice of claim 3, wherein an interior surface of the penetration probecomprises a first penetration probe wall and a second penetration probewall, wherein the first penetration probe wall and the secondpenetration probe wall are spaced apart at a first distance to define apenetration probe height, and wherein an interior surface of theanalysis chamber comprises a first analysis chamber wall and a secondanalysis chamber wall, wherein the first analysis chamber wall and thesecond analysis chamber wall are spaced apart at a second distance todefine an analysis chamber height, wherein the analysis chamber heightis less than the penetration probe height, and wherein the differentialin capillary force derives at least in part from a difference betweenthe penetration probe height and the analysis chamber height.
 5. Thedevice of claim 3, wherein at least one of the penetration probe and theanalysis chamber comprises a substance capable of enhancing ordiminishing a capillary force.
 6. The device of claim 5, wherein thesubstance is selected from the group consisting of a polymer, a resin, apowder, a mesh, a fibrous material, a crystalline material, a porousmaterial, and a combination thereof.
 7. The device of claim 6, whereinthe substance is selected from the group consisting of polyethyleneglycol, polyvinylpyrrolidone, a surfactant, a hydrophilic blockcopolymer, and polyvinylacetate.
 8. The device of claim 1, wherein thepenetration probe comprises a first penetration probe wall and a secondpenetration probe wall and wherein the analysis chamber comprises afirst analysis chamber wall and a second analysis chamber wall, andwherein the distance between the first penetration probe wall and thesecond penetration probe wall is greater than the distance between thefirst analysis chamber wall and the second analysis chamber wall.
 9. Thedevice of claim 1, wherein the penetration probe comprises a componentselected from the group consisting of a needle, a lancet, a tube, achannel, and a solid protrusion.
 10. The device of claim 1, wherein thedevice has a proximal edge, the proximal edge comprising a recess,wherein the penetration probe is positioned within the recess.
 11. Thedevice of claim 10, wherein the recess is configured to substantiallyalign with a shape of a selected dermal surface.
 12. The device of claim1, further comprising a releasable actuator, wherein the actuator iscapable of supplying a force sufficient to cause the penetration probeto penetrate a dermal layer.
 13. The device of claim 12, wherein theactuator is external to the body, and wherein upon release the actuatorpropels the body to the dermal layer.
 14. The device of claim 12,wherein the actuator is integral with the body.
 15. The device of claim14, wherein upon release the actuator propels the penetration probetoward the dermal layer.
 16. The device of claim 1, wherein the analysischamber comprises an electrochemical cell, the cell comprising a workingelectrode and a counter/reference electrode.
 17. The device of claim 1,further comprising an interface for communication with a meter.
 18. Thedevice of claim 17, wherein the interface communicates a voltage or acurrent.
 19. The device of claim 1, wherein the analysis chambercomprises a hollow electrochemical cell, the hollow electrochemical cellcomprising a working electrode, a counter or reference electrode, and anopening for admitting an analyte to the cell, the working electrodebeing spaced from the counter or reference electrode by a distance ofless than 500 μm.
 20. The device of claim 19, wherein the penetrationprobe comprises a component selected from the group consisting of aneedle, a lancet, a tube, a channel, and a solid protrusion.
 21. Thedevice of claim 19, wherein the penetration probe is capable of exertinga first capillary force and the analysis chamber is capable of exertinga second capillary force and wherein a differential exists between thefirst capillary force and the second capillary force.
 22. The device ofclaim 21, wherein the second capillary force is greater than the firstcapillary force.
 23. The device of claim 1, wherein a distal end of thepenetration probe is interfaced with the proximal end of the analysischamber.
 24. The device of claim 1, wherein a distal end of thepenetration probe is integrated with the proximal end of the analysischamber.
 25. A fluid sampling device comprising a body, the bodycomprising a dermal layer penetration probe having a penetrating end anda communicating end; an analysis chamber having a proximal end and adistal end, the analysis chamber having a volume, wherein the analysischamber comprises a hollow electrochemical cell, the hollowelectrochemical cell comprising a working electrode, a counter orreference electrode, and an opening for admitting an analyte to thecell, the working electrode being spaced from the counter or referenceelectrode by a distance of less than 500 μm; and a pre-chamber having aproximal end and a distal end, the pre-chamber having a volume, whereinthe pre-chamber is interposed between the penetration probe and theanalysis chamber such that the proximal end of the pre-chamber isadjacent the communicating end of the penetration probe and the distalend of the pre-chamber is adjacent the proximal end of the analysischamber, wherein the volume of the pre-chamber is greater than thevolume of the analysis chamber, and wherein the penetration probe is influid communication with the analysis chamber such that fluid can flowfrom the penetration probe to the analysis chamber.
 26. The device ofclaim 25, wherein the penetration probe comprises a component selectedfrom the group consisting of a needle, a lancet, a tube, a channel, anda solid protrusion.
 27. The device of claim 25, wherein the pre-chamberis capable of exerting a first capillary force and the analysis chamberis capable of exerting a second capillary force and wherein adifferential in capillary force exists between the first capillary forceand the second capillary force.
 28. The device of claim 27, wherein thesecond capillary force is greater than the first capillary force. 29.The device of claim 25, wherein the distal end of the pre-chamber isinterfaced with the proximal end of the analysis chamber.
 30. The deviceof claim 25, wherein the distal end of the pre-chamber is integratedwith the proximal end of the analysis chamber.
 31. A method formeasuring a quantity of an analyte in a fluid sample, the methodcomprising the steps of: providing a fluid sampling device, the samplingdevice comprising: a dermal layer penetration probe, having apenetrating end and a communicating end; an analysis chamber having aproximal end and a distal end, the analysis chamber having a volume,wherein the penetration probe is in fluid communication with theanalysis chamber such that a fluid sample can flow from the penetrationprobe to the analysis chamber; and a pre-chamber having a proximal endand a distal end, the pre-chamber having a volume, wherein thepre-chamber is interposed between the penetration probe and the analysischamber such that the proximal end of the pre-chamber is adjacent thecommunicating end of the penetration probe and the distal end of thepre-chamber is adjacent the proximal end of the analysis chamber, andwherein the volume of the pre-chamber is greater than the volume of theanalysis chamber; penetrating a dermal layer with the penetration probe;substantially filling the analysis chamber with the fluid sample byallowing the sample to flow from the penetration probe to the analysischamber; and measuring a quantity of an analyte in the fluid sample. 32.The method of claim 31, wherein the sample is selected from the groupconsisting of interstitial fluid and whole blood.
 33. The method ofclaim 31, wherein the analyte is selected from the group consisting ofan ion, an element, a sugar, an alcohol, a hormone, a protein, anenzyme, a cofactor, a nucleic acid sequence, a lipid, a pharmaceutical,and a drug.
 34. The method of claim 31, wherein the analyte is selectedfrom the group consisting of potassium ion, ethanol, cholesterol,glucose, and lactate.
 35. The method of claim 31, wherein a flow offluid sample to the analysis chamber is driven by a driving force,wherein the driving force comprises a force selected from the groupconsisting of a capillary force and a pressure differential.
 36. Themethod of claim 31, wherein the pre-chamber is capable of exerting afirst capillary force and the analysis chamber is capable of exerting asecond capillary force and wherein a differential in capillary forceexists between the first capillary force and the second capillary force.37. The method of claim 31, wherein the second capillary force isgreater than the first capillary force.
 38. The method of claim 31,wherein an interior surface of the pre-chamber comprises a firstpre-chamber wall and a second pre-chamber wall, wherein the firstpre-chamber wall and the second pre-chamber wall are spaced apart at afirst distance to define a pre-chamber height, and wherein an interiorsurface of the analysis chamber comprises a first analysis chamber walland a second analysis chamber wall spaced apart at a second distance todefine an analysis chamber height, wherein the analysis chamber heightis less than the pre-chamber height, wherein the pre-chamber is capableof exerting a first capillary force and the analysis chamber is capableof exerting a second capillary force, and wherein a differential in thefirst capillary force and the second capillary force derives at least inpart from a difference between the pre-chamber height and the analysischamber height.
 39. The method of claim 31, wherein at least one of thepre-chamber and the analysis chamber comprises a substance capable ofenhancing or diminishing a capillary force.
 40. The method of claim 39,wherein the substance is selected from the group consisting of apolymer, a resin, a powder, a mesh, a fibrous material, a crystallinematerial, a porous material, and a combination thereof.
 41. The methodof claim 39, wherein the substance is selected from the group consistingof polyethylene glycol, polyvinyl pyrrolidone, a surfactant, ahydrophilic block copolymer, and polyacrylic acid.
 42. The method ofclaim 35, wherein the pressure differential comprises a positivepressure applied to the analysis chamber.
 43. The method of claim 35,wherein the pressure differential comprises a negative pressure appliedfrom the analysis chamber.
 44. The method of claim 31, wherein theanalysis chamber comprises a hollow electrochemical cell, the hollowelectrochemical cell comprising a working electrode, a counter orreference electrode, and an opening for admitting an analyte to thecell, the working electrode being spaced from the counter or referenceelectrode by a distance of less than 500 μm.
 45. The method of claim 44,wherein the penetration probe comprises a component selected from thegroup consisting of a needle, a lancet, a tube, a channel, and a solidprotrusion.
 46. The method of claim 44, wherein the pre-chamber iscapable of exerting a first capillary force and the analysis chamber iscapable of exerting a second capillary force and wherein a differentialin capillary force exists between the first capillary force and thesecond capillary force.
 47. The method of claim 44, wherein the secondcapillary force is greater than the first capillary force.
 48. A methodfor measuring a quantity of an analyte in a fluid sample, the methodcomprising the steps of: providing a fluid sampling device, the devicecomprising: a dermal layer penetration probe having a penetrating endand a communicating end, the penetration probe having a volume; ananalysis chamber having a proximal and distal end, the analysis chamberhaving a volume, wherein the volume of the penetration probe is greaterthan the volume of the analysis chamber, wherein the penetration probeis in fluid communication with the analysis chamber such that a fluidsample can flow from the penetration probe to the analysis chamber;penetrating a dermal layer with the penetration probe; substantiallyfilling the analysis chamber with a fluid sample by allowing the sampleto flow from the penetration probe to the analysis chamber; andmeasuring a quantity of an analyte in the fluid sample.
 49. The methodof claim 48, wherein the sample is selected from the group consisting ofinterstitial fluid and whole blood.
 50. The method of claim 48, whereinthe analyte is selected from the group consisting of an ion, an element,a sugar, an alcohol, a hormone, a protein, an enzyme, a cofactor, anucleic acid sequence, a lipid, a pharmaceutical, and a drug.
 51. Themethod of claim 48, wherein the analyte is selected from the groupconsisting of potassium ion, ethanol, cholesterol, glucose, and lactate.52. The method of claim 48, wherein a flow of sample to the analysischamber is driven by a driving force, wherein the driving forcecomprises a force selected from the group consisting of a capillaryforce and a pressure differential.
 53. The method of claim 48, whereinthe penetration probe is capable of exerting a first capillary force andthe analysis chamber is capable of exerting a second capillary force andwherein a differential in capillary force exists between the firstcapillary force and the second capillary force.
 54. The method of claim48, wherein the second capillary force is greater than the firstcapillary force.
 55. The method of claim 48, wherein an interior surfaceof the penetration probe comprises a first penetration probe wall and asecond penetration probe wall, wherein the first penetration probe walland the second penetration probe wall are spaced apart at a firstdistance to define a penetration probe height, and wherein an interiorsurface of the analysis chamber comprises a first analysis chamber walland a second analysis chamber wall, wherein the first analysis chamberwall and the second analysis chamber wall are spaced apart at a seconddistance to define an analysis chamber height, wherein the height of theanalysis chamber is less than the height of the penetration probe,wherein the penetration probe is capable of exerting a first capillaryforce and the analysis chamber is capable of exerting a second capillaryforce and wherein a differential in capillary force exists between thefirst capillary force and the second capillary force, and wherein thedifferential capillary force derives at least in part from a differencebetween the penetration probe height and the analysis chamber height.56. The method of claim 48, wherein at least one of the penetrationprobe and the analysis chamber comprises a substance capable ofenhancing or diminishing a capillary force.
 57. The method of claim 56,wherein the substance is selected from the group consisting of apolymer, a resin, a powder, a mesh, a fibrous material, a crystallinematerial, a porous material, and a combination thereof.
 58. The methodof claim 56, wherein the substance is selected from the group consistingof polyethylene glycol, polyvinyl pyrrolidone, a surfactant, ahydrophilic block copolymer, and polyacrylic acid.
 59. The method ofclaim 52, wherein the pressure differential comprises a positivepressure applied to the analysis chamber.
 60. The method of claim 52,wherein the pressure differential comprises a negative pressure appliedfrom the analysis chamber.
 61. The method of claim 48, wherein theanalysis chamber comprises a hollow electrochemical cell, the hollowelectrochemical cell comprising a working electrode, a counter orreference electrode, and an opening for admitting an analyte to thecell, the working electrode being spaced from the counter or referenceelectrode by a distance of less than 500 μm.
 62. The method of claim 61,wherein the penetration probe comprises a component selected from thegroup consisting of a needle, a lancet, a tube, a channel, and a solidprotrusion.
 63. The method of claim 61, wherein the penetration probe iscapable of exerting a first capillary force and the analysis chamber iscapable of exerting a second capillary force and wherein a differentialin capillary force exists between the first capillary force and thesecond capillary force.
 64. The method of claim 61, wherein the secondcapillary force is greater than the first capillary force.